Mitsubishi MS-GD-VB, MSZ-GC-VA, MSH-GD-VB, MSH-GE-VB, MS-GE-VB Service Manual

SERVICE TECHNICAL GUIDE

CONTENTS

1.

MSC/MS/MSH MICROPROCESSOR CONTROL

····· 4

2. MSZ/MLZ MICROPROCESSOR CONTROL ·······11

3. MXZ MICROPROCESSOR CONTROL ··············· 24

SPLIT-TYPE AIR CONDITIONERS

No. OBT17

REVISED EDITION-G

Revision G:

• MSZ-EF·VEW -

E

, MSZ-EF·VEB -E, MSZ-

EF·VES -

E

and MXZ-C·VA -E have been

added.

Please void OBT17 REVISED EDITION-F.

CONFIDENTIAL
(FOR INTERNAL USE ONLY)

Models

MSC-GE•VB -

E

MS-GD•VB -

E

· MU-GD•VB -

E

MS-GE•VB -

E

· MU-GE•VB -

E

MSH-GD•VB -

E

· MUH-GD•VB -

E

MSH-GE•VB -

E

· MUH-GE•VB -

E

MSZ-GC•VA -

E

· MUZ-GC•VA(H) -

E

MSZ-HC•VA(B) -

E

· MUZ-HC•VA(B) -

E

MSZ-CHC•VA -

E

MSZ-FD•VA(S) -

E

· MUZ-FD•VA(H)(BH) -

E

MSZ-GE•VA -

E

· MUZ-GE•VA(H) -

E

MSZ-CGE•VA -

E

MSZ-SF•VA -

E

MSZ-EF•VEW -

E

· MUZ-EF•VE -

E

MSZ-EF•VEB -

E

· MUZ-EF•VEH -

E

MSZ-EF•VES -

E

· MXZ-B•VA -

E

MLZ-KA•VA -

E

· MXZ-C•VA -

E

2

Revision A:

• MSZ-FD·VA -

E

has been added.

Revision B:

• MS-GD·VB -E and MSH-GD·VB -E have been added.

1. MSC/MS/MSH MICROPROCESSOR CONTROL· ·······························································································4

Indoor unit models Outdoor unit models

MSC-GE20VB
MSC-GE25VB
MSC-GE35VB
MS-GD80VB MU-GD80VB
MS-GE50VB MU-GE50VB
MSH-GD80VB MUH-GD80VB
MSH-GE50VB MUH-GE50VB

1-1. COOL OPERATION ·····································································································································4
1-2. DRY OPERATION ········································································································································5
1-3. HEAT OPERATION ······································································································································5
1-4. INDOOR FAN MOTOR CONTROL ··············································································································8
1-5. AUTO VANE OPERATION ··························································································································· 8
1-6. EXPANSION VALVE CONTROL (LEV CONTROL) ··················································································10

Revision C:

• MSZ-FD50VA -

E

, MSZ-GE·VA -E, MSZ-CHC·VA -

E

and MSZ-CGE·VA -E have been added.

Revision D:

• MSC-GE·VB-E, MS-GE·VB-E, MSH-GE·VB-E, MUZ-FD50VA -E, MSZ-GE42/50VA -

E

and MSZ-CGE42/50VA -E

have been added.

Revision E:

• MSZ-GE60/71VA-E, MUZ-GE60/71VA -E, MSZ-SF15/20VA -

E

, MXZ-3B54VA -

E

, MXZ-3B68VA -E,

MXZ-4B71VA -

E

, MXZ-4B80VA -E and MXZ-5B100VA -E have been added.

Revision F:

• MXZ-2B30VA -

E

, MXZ-2B40VA -E and MXZ-2B52VA -E have been added.

Revision G:

• MSZ-EF·VEW -

E

, MSZ-EF·VEB -E, MSZ-EF·VES -E and MXZ-C·VA -E have been added.

3

2. MSZ/MLZ MICROPROCESSOR CONTROL······································································································11

Indoor unit models Outdoor unit models

MSZ-GC22/25/35VA MUZ-GC25/35VA(H)
MSZ-HC25VA MSZ-HC35VA(B) MUZ-HC25VA

MUZ-HC35VA(B)

MSZ-CHC25/35VA
MSZ-FD25/35/50VA(S) MUZ-FD25/35VA(H)(BH)

MUZ-FD50VABH

MSZ-GE22/25/35/42/50/60/71VA MUZ-GE25/35/42/50/60/71VA(H)
MSZ-CGE22/25/35/42/50VA MUZ-EF25/35/42/50VE
MSZ-EF22/25/35/42/50VEW MUZ-EF25/35VEH
MSZ-EF22/25/35/42/50VEB
MSZ-EF22/25/35/42/50VES
MSZ-SF15/20VA
MLZ-KA25/35/50VA

2-1. COOL OPERATION ··································································································································· 11
2-2. DRY OPERATION ······································································································································ 12
2-3. HEAT OPERATION ····································································································································12
2-4. AUTO CHANGE OVER ··· AUTO MODE OPERATION·············································································15
2-5. OUTDOOR FAN MOTOR CONTROL ········································································································15
2-6. AUTO VANE OPERATION ························································································································· 15
2-7. DRAIN PUMP/FLOAT SENSOR CONTROL ····························································································· 16
2-8. INVERTER SYSTEM CONTROL ···············································································································17
2-9. OPERATIONAL FREQUENCY CONTROL OF OUTDOOR UNIT ····························································21
2-10. PRE-HEAT CONTROL ·····························································································································21
2-11. EXPANSION VALVE CONTROL/LEV CONTROL ··················································································· 22
2-12. STANDBY POWER CONTROL ···············································································································23

NOTE: As for the MXZ-A type models or MU/MUH-GA type models, refer to the appropriate service technical

guide as well as this service technical guide.

3. MXZ MICROPROCESSOR CONTROL ··············································································································24

Outdoor unit models

MXZ-2B30VA MXZ-3B68VA MXZ-3C54VA MXZ-5C100VA
MXZ-2B40VA MXZ-4B71VA MXZ-3C68VA MXZ-6C120VA
MXZ-2B52VA MXZ-4B80VA MXZ-4C71VA
MXZ-3B54VA MXZ-5B100VA MXZ-4C80VA

3-1. INVERTER SYSTEM CONTROL ···············································································································24
3-2. EXPANSION VALVE CONTROL (LEV CONTROL) ··················································································28
3-3. OPERATIONAL FREQUENCY RANGE ····································································································34
3-4. HEAT DEFROSTING CONTROL ··············································································································· 36
3-5. DISCHARGE TEMPERATURE PROTECTION CONTROL ······································································36
3-6. REFRIGERANT RECOVERY CONTROL ON HEATING ··········································································36
3-7. OUTDOOR FAN CONTROL ······················································································································37
3-8. PRE-HEAT CONTROL ·······························································································································38
3-9. COOL OPERATION ···································································································································38
3-10. DRY OPERATION ······································································································································38
3-11. HEAT OPERATION ····································································································································39

4

2. Indoor fan speed control

Indoor fan operates at the set speed by FAN SPEED CONTROL button.

In AUTO the fan speed is as follows.

Initial temperature difference Fan Speed

Room temperature minus set temperature: 1.7°C or more

························································ High

Room temperature minus set temperature: between 1 and 1.7°

C ·············································Med.

Room temperature minus set temperature: less than 1°

C ·························································Low

1°C 1.7°C

3°C

3. Coil frost prevention

Temperature control

The coil frost prevention mode in the temperature control is that the indoor fan operates at the set speed and the com-

pressor stops for 5 minutes or more.

Model

Coil frost prevention

ON OFF

Indoor coil thermistor (°C) Indoor coil thermistor (°C)

MSC-GE20VB
MSC-GE25VB

4 °C or less More than 4 °C

MSC-GE35VB 0 °C or less More than 0 °C
MS-GD80VB -1 °C or less More than -1 °C
MS-GE50VB 3 °C or less More than 3 °C
MSH-GD80VB

MSH-GE50VB

1 °C or less More than 1 °C

The coil frost prevention does not work for 5 minutes after the compressor started.

Compressor
Outdoor fan

OFF

ON

(Continuously at set speed)

Indoor fan

ON

ON

OFF

Operation chart
Example

5. Discharge temperature protection (MU-GD80VB, MUH-GD80VB)

The compressor is controlled by the temperature of discharge temperature thermistor for excess rise protection of compres­sor discharge pressure.

• Compressor
When the temperature of discharge temperature thermistor goes to 120°C or more, the compressor is turned OFF. After 3
minutes since the compressor has been turned OFF, if the temperature of discharge temperature thermistor becomes 100
°C or less, the compressor is turned ON.

4. Outdoor fan speed control (MU-GD80VB, MUH-GD80VB)

Outdoor fan speed control is as follows.

Outdoor
fan speed

High
or
Med.

Indoor
fan speed

20°C 22°C

Low

30°C 33°C

High

Temperature of
ambient temperature
thermistor

Low

High
Low

1-1. COOL ( ) OPERATION

1

MSC/MS/MSH MICROPROCESSOR CONTROL

Time control

When the three conditions as follows have been satisfied for 1 hour and 45 minutes, compressor stops for 3 minutes.
a. Compressor has been continuously operating.
b. Indoor fan speed is Low or Med.
c. Room temperature is 26°C or less.
When compressor stops, the accumulated time is cancelled and when compressor restarts, time counting starts from the
beginning.
Time counting also stops temporarily when the indoor fan speed becomes High or the room temperature exceeds 26°C.
However, when two of the above conditions (b. and c.) are satisfied again, time accumulation is resumed.

-0.3°C

0.3°C

1. Thermostat control (MSC-GE20/25/35VB)
Thermostat turns ON or OFF by the difference between room temperature and set temperature

Initial temperature difference Thermostat

Room temperature minus set temperature : 0.3°C or more ················································ ON
Room temperature minus set temperature : less than -0.3°C ·············································OFF

Set temperature

Difference between room
temperature and set tem­perature during operation

Difference between room
temperature and set tem­perature during operation

5

2. Indoor fan speed control

Indoor fan operates at the set speed by FAN SPEED CONTROL button.
In Auto fan speed becomes Low.

3. The operation of the compressor and indoor/outdoor fan
Compressor operates by room temperature control and time control.
Set temperature is controlled to fall 2°C from initial room temperature.
Indoor fan and outdoor fan operate in the same cycle as the compressor.

● When the room temperature is 23°C or over:
When the thermostat is ON, the compressor repeats 8 minutes ON and 3 minutes OFF.
When the thermostat is OFF, the compressor repeats 4 minutes OFF and 1 minute ON.

● When the room temperature is under 23°C.
When the thermostat is ON, the compressor repeats 2 minutes ON and 3 minutes OFF.
When the thermostat is OFF, the compressor repeats 4 minutes OFF and 1 minute ON.

Set temperature is as shown on the right chart.
The system for dry operation uses the same refrigerant circuit as the
cooling circuit.
The compressor and the indoor fan are controlled by the room tem­perature.
By such controls, indoor flow amounts will be reduced in order to
lower humidity without much room temperature decrease.

DRY operation will not work when the room temperature is 13°C or
below.

1-2. DRY ( ) OPERATION

35

30

25

20

15

10

10 15 20 25 30 35

Set temperature

Initial room temperature

Set temperature and
initial room temperature in DRY mode

Thermostat

Indoor fan

Outdoor fan
Compressor

ON

8 minutes

3

minutes

ON

OFFOFF

OFF

OFF

OFF

OFF

OFF

OFF

ON

ON

ON

ON

ON

ON

Operation time chart
Example
When the room temperature is 23°C or over:

4. Coil frost prevention

• The operation is the same as coil frost prevention during COOL mode.

• The indoor fan operates at the set speed and the compressor does not operate for 5 minutes because the coil frost pre­vention has priority.

1

minute

4

minutes

-0.3°C

0.3°C

1. Thermostat control (MSC-GE20/25/35VB)
Thermostat turns ON or OFF by the difference between room temperature and set temperature.

Initial temperature difference Thermostat

Room temperature minus set temperature : 0.3°C or more ··············································ON
Room temperature minus set temperature : less than -0.3°C ··········································· OFF

Set temperature

Difference between room
temperature and set tem­perature during operation

-0.3°C

0.3°C

Set temperature

Difference between room
temperature and set tem­perature during operation

1. Thermostat control (MSC-GE20/25/35VB)
Thermostat turns ON or OFF by the difference between room temperature and set temperature.

Initial temperature difference Thermostat

Room temperature minus set temperature : less than -0.3°C ·············································ON
Room temperature minus set temperature : 0.3°C or more ················································OFF

1-3. HEAT ( ) OPERATION (MSC-GE20/25/35VB, MSH-GD80VB, MSH-GE50VB)

6

(3) Warm air control

When compressor starts in heating operation or after defrosting, the fan changes the speed due to the indoor coil ther­mistor temperature to blow out warm air.
After releasing of cold air prevention, when the indoor coil thermistor temperature is 37°C or above, the fan speed shifts
to the set speed, and when the fan speed is changed by the remote controller, the fan speed is the set speed.
When the indoor coil thermistor temperature is less than 37°C, the fan speed is controlled by time as below.
<Time condition> <Indoor fan speed>
Less than 2 minutes ······················· Low
2 minutes to 4 minutes ···················Med.
4 minutes or more ··························High
The upper limit of the fan speed in MANUAL is the set speed.
The upper limit of the fan speed in AUTO is the speed decided by the indoor fan speed control. (Refer to 1-3.2.(1).)
If the thermostat turns OFF, this operation changes to flow soft control. (MSH-GD80VB, MSH-GE50VB)

(4) Flow soft control (MSH-GD80VB, MSH-GE50VB)

After the thermostat turns OFF, the indoor fan operates at Very Low.
NOTE: When the thermostat turns ON, the fan operates at the set speed. Due to the cold air prevention control, the fan

does not start at set speed until the indoor coil thermistor reads 22°C or more.

3. Outdoor fan speed control (MUH-GD80VB)

Outdoor fan speed control is as follows.

13°C 18°C

Outdoor
fan speed

High

Low

T

emperature of
ambient temperature
thermistor

(2) Cold air prevention control

When the compressor is not operating (MSC-GE20/25/35VB):
( ) If the temperature of indoor coil thermistor RT12 is 0°C or less, the fan stops.
( ) If the temperature of indoor coil thermistor RT12 is more than 0°C, the fan operates at Very Low.

When the compressor is operating:
( ) If the temperature of RT12 is 22°C or more, the fan operates at set speed.
( ) If the temperature of RT12 is less than 22°C and
( ) if the temperature of room temperature thermistor RT11 is 15°C or less, the fan stops.
( ) if the temperature of room temperature thermistor RT11 is more than 15°C, the fan operates at Very Low.

NOTE : If the temperature of RT12 reads from 18°C to 22°C at the air conditioner stating and also after defrosting, this

control works.

Released

Cold Air Prevention

18°C 22°C

Fan speed
Set speed

Very Low or stop

(MSH-GD80VB, MSH-GE50VB) Initial temperature difference Fan speed

Set temperature minus room temperature: 2°C or more ·····················································High
Set temperature minus room temperature: between 1 and 2°C········································· Med.
Set temperature minus room temperature: less than 1°C ····················································Low

1°C 1.7°C

4°C

2°C

2. Indoor fan speed control

(1) In AUTO the fan speed
(MSC-GE20/25/35VB)
Indoor fan speed at set speed by FAN SPEED CONTROL button.

Initial temperature difference Fan speed

Set temperature minus room temperature: 1.7°C or more ·················································High
Set temperature minus room temperature: between 1 and 1.7°

C ·································

Med.

Set temperature minus room temperature: less than 1°

C ·············································

Low

1°C

1.7°C

3°C

Difference between room
temperature and set tem­perature during operation

Difference between room
temperature and set tem­perature during operation

7

4. High pressure protection (MUH-GD80VB, MUH-GE50VB)

During heating operation, the outdoor fan and the compressor are controlled by the temperature of indoor coil thermistor
for excess rise protection of compressor discharge pressure.

• Outdoor fan
When the temperature of indoor coil thermistor goes to 55°C or more, the outdoor fan is turned OFF.
When the temperature of indoor coil thermistor becomes 52°C or less, the outdoor fan is turned ON.

• Compressor
When the temperature of indoor coil thermistor goes to 75°C or more, the compressor is turned OFF.
3 minutes after the compressor is turned OFF and if the temperature of indoor coil thermistor becomes 75°C or less, the

compressor is turned ON.

NOTE: During the high pressure protection and for 10 seconds after high pressure protection, defrosting of outdoor heat

exchanger is not detected by the defrost thermistor.

5. Defrosting

Defrosting of outdoor heat exchanger is controlled by deicer P.C. board, with detection by the defrost thermistor.
(1) Starting conditions of defrost
When all conditions of a) ~ c) are satisfied, the defrosting operation starts.

a) Under the heat operation, the compressor cumulative operation time exceeds 40 minutes without the defrosting opera-

tion working.
b) The defrost thermistor reads -3°C or less.
c) After releasing the high pressure protection 4 minutes and 10 seconds have elapsed.

(2) Releasing conditions of defrost
When the condition d) or e) is satisfied, the defrosting operation stops.

d) The defrost thermistor reads 10°C (MUH-GE50VB) /13°C or more (MUH-GD80VB).
e) The defrosting time exceeds 10 minutes.

(3) Defrosting time chart

Defrost thermistor
13°C or more (MUH-GD80VB)
10°C or more (MUH-GE50VB)

-3°C or less
Outdoor 52C

contactor
(Compressor)

X62
(R.V. coil)

SR61
Outdoor fan

Defrost
counter

Indoor fan

Indoor vane

ON
OFF

ON
OFF

ON
OFF

ON
OFF

ON

OFF
Horizontal

Set position

Maximum 10 minutes

30 seconds

15 seconds

30 seconds

5 seconds

NOTE

Very Low

NOTE: • When the indoor coil thermistor reads above 18°C, indoor fan operates at Very Low for 30 seconds.

• When the indoor coil thermistor reads 18°C or less, the indoor fan stops.

8

1-4. INDOOR FAN MOTOR CONTROL

(1) Rotational frequency feedback control
The indoor fan motor is equipped with a rotational frequency sensor, and outputs signal to the microprocessor to feed-

back the rotational frequency. Comparing the current rotational frequency with the target rotational frequency (High,
Med., Low), the microprocessor controls SR141 and adjusts fan motor electric current to make the current rotational
frequency close to the target rotational frequency. With this control, when the fan speed is switched, the rotational fre­quency changes smoothly.

High

Rotational frequency

High

time

Med.

Low

(2) Fan motor lock-up protection

When the rotational frequency feedback signal has not output for 12 seconds, (or when the microprocessor cannot
detect the signal for 12 seconds) the fan motor is regarded locked-up. Then the electric current to the fan motor is shut­off. 3 minutes later, the electric current is applied to the fan motor again. During the fan motor lock-up, the OPERATION
INDICATOR lamp flashes ON and OFF to show the fan motor abnormality.

1-5. AUTO VANE OPERATION (MSC, MSH)

1. Horizontal vane

(1) Cold air prevention in HEAT operation
When any of the following conditions occur in HEAT operation, the vane angle changes to Angle 1 automatically to pre-

vent cold air blowing on users.
Compressor is not operating.
Defrosting is performed.
Indoor coil thermistor reads 24°C or below.
Indoor coil thermistor temperature is rising from 24°C or below until it reaches 28°C.

NOTE1: If the temperature of the indoor coil thermistor reads from 24 to 28°C at the air conditioner starting, this control

works.

NOTE2: When 2 or more indoor units are operated with multi outdoor unit, even if any indoor unit turns thermostat OFF, this

control does not work in the indoor unit.

Released

Cold Air Prevention

24°C 28°C

Angle 1

Horizontal vane

Set position

Indoor coil thermistor temperature

9

(2) ECONO COOL ( ) operation (ECONOmical operation)
When ECONO COOL button is pressed in COOL mode, set temperature is automatically set 2°C higher.
Also the horizontal vane swings in various cycle according to the temperature of indoor heat exchanger.
SWING operation makes you feel cooler than set temperature. So, even though the set temperature is higher, the air

conditioner can keep comfort. As a result, energy can be saved.

To cancel this operation, select a different mode or press one of the following buttons in ECONO COOL operation:

ECONO COOL, VANE CONTROL or LONG button.
NOTE: ECONO COOL operation does not work in COOL mode of “I FEEL CONTROL”.
<SWING operation>
In swing operation of ECONO COOL operation mode, the initial airflow direction is adjusted to “Horizontal”.

According to the temperature of indoor coil thermistor at starting of this operation, next downward blow time is decided.

Then when the downward blow has been finished, next horizontal blow time is decided.
For initial 10 minutes the swing operation is performed in table G~H for quick cooling.
Also, after 10 minutes when the difference between set temperature and room temperature is more than 2°C, the swing

operation is performed in table D ~ H for more cooling.
The air conditioner repeats the swing operation in various cycle as follows.

Temperature of

indoor coil thermistor(°C)

Downward blow time

(second)

Horizontal blow time

(second)

A

15 or less 2 23

B

15 to 17 5 20

C

17 to 18 8 17

D

18 to 20

11 14

E

20 to 21 14 11

F

21 to 22 17 8

G

22 to 24 20 5

H

More than 24 23 2

10

NOTE : Opening increases and decreases to be in the target discharge temperature during operation.

Opening
completely

Positioning

Power ON

Initial opening

Standard opening

Remote
controller
ON

Operation

Thermostat
OFF

Standard opening

Thermostat
ON

Opening in stop

Operation

Opening in stop

Remote
controller
OFF

Opening
completely

Remote
controller
ON

Positioning

Standard opening

Operation

Time

LEV opening

Initial opening

Initial opening

Open

Close

(2) LEV time chart

1-6. EXPANSION VALVE CONTROL (LEV CONTROL) (MU-GD80VB, MUH-GD80VB)

LEV (Expansion valve) is controlled by “Thermostat ON” commands given from the unit.

Standard

specification

Control range Minimum: 54 pulse, Maximum: 500 pulse
Drive speed 30 ~ 90 pulse/second

Opening set The setting is always in opening direction.

(To close LEV, it is closed to the pulse smaller than the one set finally.
Then LEV is opened to the final setting pulse.)

General operation

Stop of indoor unit Opening in stop: 150 pulse → LEV opening is set to become 500 pulse after 3 min-

utes.

Remote controller ON LEV positioning (LEV is closed completely at once)
Power ON (Breaker ON) LEV is positioned. However, afterwards, LEV is not positioned when the remote

controller is turned ON for the first time after the power ON.

Approximately for 2 minutes after
compressor has started.

Opening is set by the initial opening.
(Initial opening is set according to each operation mode and outer temperature con­ditions.)

Approximately 2 to 13 minutes (for
11 minutes) after compressor has
started.

Opening is set by standard opening.
(Standard opening is set according to each operation mode and outer temperature
conditions.)

13 minutes after compressor has
started.

LEV opening is corrected every 2 minutes so that discharge temperature becomes
the target discharge temperature.
(When the discharge temperature is lower than the target temperature: LEV is cor­rected in closed direction, when the discharge temperature is higher than the target
temperature: LEV is corrected in opening direction.)

Thermostat OFF

Opening in stop: 150 pulse → LEV is set to the initial opening after about 3 minutes.

Thermostat ON

Same as the starting of compressor operation

Remote controller OFF

Opening in stop: 150 pulse → LEV is set so that the opening is opened completely
at the speed of 4 pulse every 5 seconds in opening after about 3 minutes.

Operation mode Target discharge temperature (°C)
HEAT (MUH-GD80VB) 85
COOL (Normal) 80
COOL (∆RT is less than 2°C, or ∆RT is 2°C or more and less than 3°C.) 70
COOL (∆RT is 3°C or more.) 65

NOTE: When the discharge temperature is 50°C or less on the cool operation, or is 49°C or less on heat operation

(MUH-GD80VB), LEV opening is set in 54 pulse.
When this state continues for 20 minutes, the compressor is stopped and restarts in 3 minutes.
When the compressor is stopped, the indoor unit indicates the abnormality of refrigerant system and stops.

(OPERATION INDICATOR lamp is 10-time flashing ON and OFF.)

(1) Control data
Reference value of target discharge temperature

11

1. Thermostat control (MSZ)

Thermostat turns ON or OFF by the difference between room temperature and set temperature.

2-1. COOL ( ) OPERATION

2. Indoor fan speed control

Indoor fan operates continuously at the set speed by FAN SPEED CONTROL button regardless of the thermostat’s OFF­ON. [When the thermostat turns OFF, the indoor fan stops running to reduce power consumption.
After that, the indoor fan stops for 60 seconds and then operates at Very Low for 10 seconds to sense accurate room
temperature. The indoor fan alternates ON and OFF at this interval while the thermostat is OFF.
When the room temperature rises and the thermostat is ON, the indoor fan starts running according to the settings on the
remote controller. (MSZ-GE60/71VA)]
[When the thermostat turns OFF, the indoor fan operates at very Low to reduce power consumption. When the room tem­perature rises and the thermostat turns ON, the indoor fan starts running according to the settings on the remote controller
(MSZ-EF)]
In AUTO, the fan speed is as follows.

3. Coil frost prevention (MSZ)

The compressor operational frequency is controlled to prevent the temperature of indoor heat exchanger from falling excessively.
The compressor is turned OFF for 5 minutes when the temperature of indoor coil thermistor continues 3°C or less for
5 minutes or more.
The indoor fan maintains the actual speed at the time.

4. Low outside temperature operation (MUZ-GC/FD/GE/EF)
MUZ-GC25

If the outside temperature falls to 17°C or less during operation in COOL mode, the unit will switch to the low outside
temperature operation mode.
Each outdoor actuator (compressor/fan/LEV) is operated in the exclusive control, which is different from one of normal cool
operation.
Especially, fan motor does not operate continuously to maintain sufficient cooling capacity.
<Operation>

(1) Outdoor fan control
Basically, outdoor unit (compressor) operates with outdoor fan OFF.
But, when any of following conditions are satisfied, the outdoor fan turns ON for about 5 seconds.
a). The defrost thermistor reads 45°C or more.
b). The fin temperature thermistor reads 60°C or more.
(2) LEV (expansion valve) control
In normal cool operation, the opening degree of expansion valve is corrected according to the discharge temperature.
But in this mode it is fixed to the value corresponding to the operation frequency of compressor.
(3) Dew drop prevention
When the ambient temperature thermistor reads -20°C or less, as coil frost or dew drop from indoor unit may occur, the

compressor turns OFF with the outdoor fan ON for prevention of it.

(4) Outdoor temperature detecting control
To detect the exact outdoor temperature in this mode, the compressor turns OFF, but the outdoor fan stays ON for
3 minutes once every 1 hour. If the outdoor temperature rises over 19°C, the unit goes back to the normal COOL mode.
If the outside temperature stays below 19°C, the unit continues to run in the low outside temperature operation mode.

MUZ-GC35, FD, GE, EF

If the outside temperature falls to 18°C or less during operation in COOL mode, the unit will switch to the low outside
temperature operation mode.
<Operation>
(1) Outdoor fan control
The outdoor fan rotation speed slows down to maintain sufficient cooling capacity.

NOTE: Even when the unit is in the "thermostat-off" status under the low outside temperature operation mode, the

outdoor fan rotation does not stop.
(2) Dew drop prevention
When the ambient temperature thermistor reads the following temperature, as coil frost or dew drop from indoor unit

may occur, the compressor turns OFF with the outdoor fan OFF for prevention of dew drop.

• -20°C or less (MUZ-GC35, FD25/35, GE25/35/42, EF25/35/42)

• -15°C or less (MUZ-FD50)

• -12°C or less (MUZ-GE50/60/71,EF50)
(3) Outdoor temperature detecting control
To detect the exact outdoor temperature in this mode, the compressor turns OFF but the outdoor fan stays ON for

3 minutes once every 1 hour. If the outdoor temperature rises over about 18°C, the unit goes back to the normal COOL mode.
If the outside temperature stays below about 18°C, the unit continues to run in the low outside temperature operation mode.

Other protections work as well as in the normal COOL mode.

ON

-1°C or more

Less than -1°C

-1°C

-0.75°C

Room temperature minus
set temperature (During operation)

Room temperature minus
set temperature (Initial)

Thermostat

OFF

High
Med.
Low

1.75°C

3°C

1°C

Fan speed

Room temperature minus
set temperature (During operation)

Room temperature minus
set temperature (Initial)

Between 1 and 1.75°C
Less than 1°C

1.75°C or more

2

MSZ/MLZ MICROPROCESSOR CONTROL

12

2. Indoor fan speed control

Indoor fan operates continuously at the set speed by FAN SPEED CONTROL button regardless of the thermostat’s OFF­ON. [When the thermostat turns OFF, the indoor fan stops running to reduce power consumption.
After that, the indoor fan stops for 60 seconds and then operates at Very Low for 10 seconds to sense accurate room
temperature. The indoor fan alternates ON and OFF at this interval while the thermostat is OFF.
When the room temperature rises and the thermostat is ON, the indoor fan starts running according to the settings on the
remote controller. (MSZ-GE60/71VA)]
[When the thermostat turns OFF, the indoor fan operates at very Low to reduce power consumption. When the room tem­perature rises and the thermostat turns ON, the indoor fan starts running according to the settings on the remote controller
(MSZ-EF)]
In AUTO, the fan speed is as follows.

3. Coil frost prevention (MSZ)

Coil frost prevention is as same as COOL mode. (2-1.3.)
The indoor fan maintains the actual speed of the moment. However, when coil frost prevention works while the compressor
is not operating, its speed becomes the set speed.

4. Low outside temperature operation (MUZ-GC/FD/GE/EF)

Low outside temperature operation is as same as COOL mode. (2-1.4.)

NOTE: When 2 or more indoor units are operated with a multi type outdoor unit, the fan operates intermittently at Very Low or

stops in the thermostat-OFF units while at least one unit is thermostat-ON.

High
Med.
Low

1.75°C

2.5°C

1°C

Fan speed

Room temperature minus
set temperature (During operation)

Room temperature minus
set temperature (Initial)

Between 1 and 1.75°C

Less than 1°C

1.75°C or more

2-2. DRY ( ) OPERATION

Set temperature is as shown on the right chart.
The system for dry operation uses the same refrigerant circuit as the
cooling circuit.
The compressor and the indoor fan are controlled by the room tem­perature.
By such controls, indoor air flow amounts will be reduced in order to
lower humidity without much room temperature decrease.

35

30

25

20

15

10

10 15 20 25 30 35

Set temperature (°C)

Initial room temperature (°C)

Set temperature and
initial room temperature in dry mode

1. Thermostat control (MSZ)

Thermostat turns ON or OFF by the difference between room temperature and set temperature.

ON
OFF

-2°C

-1.75°C (MSZ-GE25/35/42,EF25/35/42/50)

-2°C

-0.75°C (Other models)

Thermostat

Room temperature minus
set temperature (Initial)

Room temperature minus
set temperature (During operation)

-2

°C or more

Less than -2

°C

2-3. HEAT ( ) OPERATION

1. Thermostat control (MSZ)

Thermostat turns ON or OFF by the difference between room temperature and set temperature.

ON

1°C or more

Less than 1°C

0.75°C

1°C (MSZ-GE60/71,EF25/35/42/50)

Room temperature minus
set temperature (During operation)

Room temperature minus
set temperature (Initial)

Thermostat

OFF
ON

2°C or more

Less than 2°C

1.75°C

2°C (Other models)

OFF

2. Indoor fan speed control

(1) Indoor fan operates at the set speed by F

AN SPEED CONTROL button.

In Auto, the fan speed is as follows.

High
Med.
Low

Fan speed

Room temperature minus
set temperature (During operation)

Room temperature minus
set temperature (Initial)

Between 0.25 and 2°C

Less than 0.25°C

2°C or more

0.25°C

1.75°C

2°C

4°C